(a) Field of the Invention
The present invention relates to a wireless portable Internet system. More particularly, the present invention relates to a method for searching and releasing an abnormal subscriber station in a wireless portable Internet system, and an apparatus using the same.
(b) Description of the Related Art
As next-generation communication technology, a wireless portable Internet further provides mobility to a local data communication system, such as a conventional wireless local area network (LAN), using a stationary access point.
A wireless portable Internet system developed by the IEEE 802.16 group supports mobility of a subscriber station when the subscriber station moves from a cell served by a first base station to another cell served by a second base station so that it provides seamless data communication services. A mobile communication system including such a wireless portable Internet is being developed to a communication system that can support a voice service as well as a high speed packet data service.
In the wireless portable Internet system, a subscriber station must perform a ranging function so as to access an access point (AP), that is, a base station. The ranging function in the wireless portable Internet system adjusts transmit power, transmit timing, and frequency offset of an uplink so that the AP can successfully receive data transmitted from the subscriber station. Therefore, when the subscriber station periodically transmits a code division multiple access (CDMA) code, the base station receives the CDMA code, measures and adjusts transmit power, transmit timing, and frequency offset, and transmits an adjustment value to the subscriber station. Herein, the adjustment value includes transmit power, transmit timing, and frequency offset that have been adjusted to be included within a range for precise data receiving.
As described, although the subscriber station periodically reports a status of the subscriber station to the base station by using the ranging function, the base station does not know whether a currently accessing subscriber station abnormally releases a call, and accordingly, the base station continuously manages resources for the subscriber station, thereby causing inefficient resource management and radio resource waste.
Therefore, an algorithm for checking a status of a subscriber station by using a subscriber status check message so as to check the status of a currently connected subscriber is required. However, a current specification of the IEEE 802.16e does not define a message for checking the status of a subscriber station.
Even if a message for checking a status of a subscriber station existed, a load to check a subscriber station status may increase when too many subscriber stations are currently being served, and radio resource waste may occur when transmitting the message to all subscriber stations.